In French patent application Ser. No. 80 04313 dated Feb. 27, 1981 and its Addition Ser. No. 80.09781 dated Apr. 30, 1980, is disclosed an oleo-pneumatic accumulator made of two substantially semispherical shells, assembled to each other with interposition of a flexible membrane and a cylindrical spacer wedge, the two shells and the wedge being maintained pressed against each other by an outer belt subjected, before assembly, to a previous prestress generating a clamping effort superior to the maximum separation effort of said parts when the accumulator thus formed is subjected to the maximum utilization pressure.
On the other hand, it is known from French patent application Ser. No. 81.00740 filed on Jan. 16, 1981 by the same applicant how to manufacture a hydraulic accumulator by means of a tubular central body sealed at both ends by a plug.
The prestressed accumulators according to French patent application Ser. No. 80.04319 and its Addition Ser. No. 80.09781 provide excellent results, but offer various disadvantages. First of all, their mass production is difficult since it requires a rather complex mechanism which is time consuming when used for setting the cylindrical belt surrounding the parts under a preliminary stress. After, it appears that when the effort for providing the preliminary tension is released, a part of the prestress is absorbed by a relative contraction of the wedge and by a deformation, even very slight, of the threadings. The result is a fairly variable value of the prestress remaining after assembly of the parts.
The accumulators disclosed in patent application Ser. No. 81.00740 offer the considerable advantage of being very economical to manufacture, but they have the disadvantage of not resisting the high utilization pressures and therefore of being unusable in hydraulic circuits working at high or very high pressure.